The invention concerns a carriage intended to be placed transversely between two lateral girders substantially parallel to each other, the carriage being arranged so as to be able to be moved in a longitudinal direction parallel to the girders. The invention also concerns a gantry comprising two lateral girders substantially parallel to each other, as well as such a carriage.
Such carriages and gantries are used in factories, warehouses, etc. for handling objects, for example between various machining and/or storage stations. Generally the carriage comprises on the one hand a stirrup at each of its lateral end parts, the stirrups being intended to cooperate with the lateral girders of the gantry, and on the other hand a movable central girder placed between the stirrups and fixed to these, the girder being able to carry various tools or members for gripping objects. One or more motors enable the carriage to move longitudinally.
According to a first embodiment, a single central motor is provided on the carriage, provided with two lateral transmission shafts and pinions, in order to allow the driving of the carriage along the lateral girders. However, this solution is technically difficult to implement and may prove to be costly.
According to a second embodiment, two separate motors each drive one of the two stirrups of the carriage. Means of synchronising the two motors must then be provided, which gives rise to not insignificant additional cost and requires increased maintenance of the installations. In addition, despite these synchronisation means, there remain risks that the stirrups may not be moved strictly simultaneously and at the same speed. As a result the carriage may not remain perfectly transverse and risks being locked aslant between the lateral girders. This may occur even if the offset between the positions of the two stirrups is only a few millimeters.
In addition, having regard to the imperfect synchronisation of the two stirrups, such gantries do not allow movement of the carriage with the required precision, around one millimetre. Moreover, whatever the method of driving the stirrups and its performance, there exists another cause that may result in jamming of the carriage or impair the precision of the gantry. It is a case of lack of parallelism between the lateral girders. This may be due to the actual manufacture of the girders, where it is difficult to guarantee straightness because of their great length, around 20 meters for example. This defect may also stem from the deformation of the girders over time, after several months or several years of use of the gantry.
The invention aims to resolve the problems posed by the prior art by proposing an economical carriage and gantry guaranteeing excellent precision of movement of the carriage without any risk of jamming between the lateral girders, despite the non-parallelism of the lateral girders or imperfect synchronisation of the movement of the two stirrups. To this end, and according to a first aspect, the invention concerns a carriage intended to be placed substantially transversely between first and second lateral girders substantially parallel to each other, the carriage comprising:
a stirrup at each of its lateral end parts, a first stirrup being able to cooperate with the first lateral girder and a second stirrup being able to cooperate with the second lateral girder so as to allow the movement of the carriage in a longitudinal direction substantially parallel to the lateral girders;
a central girder placed between the stirrups;
a first connection means arranged between a first lateral end of the central girder and the first stirrup and second connection means arranged between a second lateral end of the central girder and the second stirrup, the connection means being arranged to allow the movement of one stirrup with respect to the other, according to six degrees of freedom, with limited amplitude.
Because the central girder is not being fixed to the stirrups, the stirrups can move with respect to each other, causing a deformation of the carriage (movement of the central girder with respect to the stirrups). The means of connection between the lateral ends of the central girder and the stirrups makes it possible to accommodate and compensate for any errors in synchronisation of the motors or deformations of the lateral girders. The movement of the central girder with respect to the stirrups thus makes it possible to obtain more flexibility and prevent locking of the carriage, despite the constant movement of one stirrup with respect to the other.
According to the invention, the first connection means can comprise a swivel connection and the second connection means a vertical support and transverse sliding means, the support and the transverse sliding means being arranged so as to allow the rotation movement of the central girder with respect to the first stirrup about longitudinal, transverse and vertical axes with limited amplitude. According to other characteristics the transverse sliding means can include means of limiting the amplitude of the rotation of the central girder with respect to the first stirrup about longitudinal, transverse and vertical axes.
According to one possible embodiment, the first connection means also comprise transverse sliding means situated at a distance from the swivel connection, the transverse sliding means being arranged so as to allow the rotation movement of the central girder with respect to the first stirrup about longitudinal, transverse and vertical axes with limited amplitude. For example, at least one of the transverse sliding means comprises:                on the one hand a piece having a U shape, the arms of which are situated in a substantially horizontal plane and directed transversely towards the central girder, the ends of the arms being fixed rigidly to a stirrup of the carriage;        on the other hand a rod fixed rigidly to the central girder and extending orthogonally to the U-shaped piece, the rod being arranged so as to be inserted in the space formed between the arms of the U-shaped piece with clearance so as to allow the transverse sliding of the central girder with respect to the end part of the carriage and to allow the rotation of the central girder with respect to the first stirrup about longitudinal, transverse and vertical axes according to a certain amplitude, by virtue of the swivel connection.        
The second stirrup can comprise two vertically aligned U-shaped pieces situated at a distance from each other, the central girder being provided with two aligned vertical rods arranged so as to each to be inserted in one of the U-shaped pieces. For example, the first stirrup comprises a concave housing, and a convex piece with a shape complementary to that of the housing is rigidly fixed to the central girder so as to be able to cooperate with the housing in order to form the swivel connection.
According to one possible embodiment, the first stirrup comprises on the one hand a concave housing with a substantially vertical axis and on the other hand a U-shaped piece, and a central girder is provided with a vertical rod arranged so as to be inserted in the U-shaped piece so as to be placed so as to be substantially aligned with the axis of the concave housing. For example, a first intermediate piece is rigidly fixed to each of the two stirrups and a second intermediate piece is rigidly fixed to each of the lateral ends of the central girder, the means of connection between the girder and the stirrups being carried by the intermediate pieces.
According to a second aspect, the invention concerns a gantry comprising first and second substantially parallel lateral girders and a carriage as previously described, the carriage being placed substantially transversely between the lateral girders, and comprising a stirrup at each of its end parts, a first stirrup being able to cooperate with the first lateral girder and a second stirrup being able to cooperate with the second lateral girder so as to allow the movement of the carriage in a longitudinal direction substantially parallel to the lateral girders.